Freeze-drying is mainly utilized for preserving temperature sensitive products while maintaining certain desirable characteristics of the products. Freeze-drying is extensively employed in the fields of pharmacology, biology and medicine.
The freeze-drying process involves removing substantially all of the water from the product to be preserved. The standard freeze-drying process can be generally summarized as follows:
First, the product is frozen in order to convert the water present in the product to ice. Next, in a main drying step, the product is subjected to a vacuum of approximately 10.sup.- mbar, which causes sublimation of the ice to occur.
The main drying step is followed by a supplemental drying step, in which the adsorptively bonded water is removed in order to obtain an extremely low level of residual moisture. During supplemental drying, the product is heated to a predetermined temperature under a vacuum of approximately 10.sup.-3 mbar.
Since freeze-drying is usually practiced as a batch process, efforts have been undertaken to process the largest possible batches within the constraints of available equipment. In present practice, the monetary value of such batches is extremely high, often exceeding one million German marks (approximately $580,000.00). Therefore, from an economic standpoint alone, it is important to minimize the potential for loss of such batches due to contamination of the product.
A significant potential for product contamination exists during loading and unloading of the product containers from the freeze-drying process chamber. Loading and unloading of the containers is usually performed manually. The containers holding the product to be dried (up to 100,000 bottles per batch) are conveyed from a filling station to the freeze-drying equipment, and are manually placed onto placement surfaces within the chamber. The containers are loaded and unloaded using platters that remain in the freeze-drying chamber during the freeze-drying process.
Since the containers having the product to be freeze-dried are initially open, it is of particular importance that loading be performed under extremely clean conditions. Before loading, the containers are loosely covered with a plug having a water vapor escape passage. After the containers have been loaded onto the placement surfaces, the freeze-drying process is implemented as described hereinabove. After completion of the process the placement surfaces, which generally vertically overlie one another within the chamber, are brought together within the chamber, thus causing the plugs to close the containers at a predetermined pressure.
British Patent No. GB-A-21 85 969 discloses an apparatus for loading and unloading freeze-drying equipment. In this apparatus, containers are continuously supplied via a conveyor belt, and are successively placed onto transfer plates that are moved into the freeze-drying chamber in succession. With each transfer, only a relatively small number of containers is introduced into the freeze-drying chamber. Consequently, loading of the containers into the freeze-drying chamber is more time consuming than is desirable. Furthermore, the apparatus necessitates contact between the transfer plates and the upper sides of the placement surfaces, since the transfer plates must rest on the placement surfaces in order to avoid upsetting the containers during transfer. Such contact produces a significant degree of friction, which not only generates heat, but may lead to an abrasion of contact surfaces which increases the potential for contamination of the product.
It is therefore apparent that there exists a need for a method and apparatus for loading and unloading containers into freeze-drying equipment that will simplify and accelerate the handling of large batches of containers, while simultaneously reducing the risk of product contamination.